Well crap, if you want to actually talk seriously for a second, the overall service stats quoted above don't take into account the "quality" factor. I'm not going to take the time to verify with a hard analysis, but I'm fairly certain we'd find that the average ranking of the players Fed has played are a noticeable notch up the scale from Raonic's opponents. That's a factor of both Fed playing higher quality tournaments on average, and also going deeper in the draw on average. Those higher quality players make it more difficult for Fed to pad his stats on service effectiveness, and even ace counts (I'll hypothesize that better players on average read incoming serves better and get aced less).

I don't think any of the big 4 are afraid of Raonic's service game. They know that to be the best they have to absorb the best of what the field has to throw at them. That being said, you can't tell me that anyone is really happy going in there against the Raonic service game. Even with limited (but improving) tools to back up his delivery, he's already better than Karlovic ever was, and I remember all the talk from the top players about how awkward it was to play Karlovic before he started slipping in recent years.

The number of matches when opponents have really started to get a hold on Raonic's service have been very few and far between. Muzza got on top of it at USO and all credit to him, but the majority of Raonic service games for the foreseeable future are going to be mostly on his racket in terms of the outcome.

Regardless of the "opposition", Raonic's serve is still vastly superior to Federer's